1. Field of the Invention
The present invention relates to an organic anti-reflective coating (xe2x80x9cARCxe2x80x9d) material which allows the stable formation of ultrafine patterns suitable for 64 M, 256 M, 1 G, 4 G and 16 G DRAM semiconductor devices. More particularly, the present invention relates to an organic anti-reflective coating material which contains a chromophore with high absorbance at the wavelengths useful for submicrolithography. A layer of said anti-reflective material can prevent the back reflection of light from lower layers of the semiconductor chip, as well as eliminate the standing waves caused by light and thickness changes of the photoresist layer itself, while conducting a submicrolithographic process using a 248 nm KrF, 193 nm ArF or 157 nm F2 laser. Also, the present invention is concerned with an anti-reflective coating composition comprising such a material, an anti-reflective coating made therefrom and a preparation method thereof.
2. Description of the Prior Art
During a submicrolithographic process, one of the most important processes for fabricating highly integrated semiconductor devices, there inevitably occur standing waves and reflective notching due to the optical properties of lower layers on the wafer and to changes in the thickness of the photosensitive film applied thereon. In addition, the submicrolithographic process generally suffers from a problem of the CD (critical dimension) being altered by the diffracted light and reflected light from the lower layers.
To overcome these problems, it has been proposed to introduce a film, called an anti-reflective coating, between the substrate and the photosensitive film to prevent light reflection from the lower layer. Generally, anti-reflective coatings are classified into xe2x80x9corganicxe2x80x9d and xe2x80x9cinorganicxe2x80x9d by the materials used and into xe2x80x9cabsorptionxe2x80x9d and xe2x80x9cinterferencexe2x80x9d by the mechanisms involved. In microlithographic processes using an I-line light source (365 nm in wavelength), inorganic anti-reflective coatings are usually used, for example TiN or amorphous carbon coatings are applied when advantage is taken of an absorption mechanism, and SiON coatings are applied when an interference mechanism is desired. The SiON anti-reflective coatings are also adapted for submicrolithographic processes which uses KrF light sources.
Recently, extensive and intensive research has been and continues to be directed to the application of organic anti-reflective coatings for such submicrolithography. In view of the present development status, organic anti-reflective coatings, to be useful, must satisfy the following fundamental requirements:
First, peeling of the photoresist layer due to dissolution in solvents should not take place when conducting a lithographic process with an organic anti-reflective coating. In this regard, the organic anti-reflective coating materials have to be designed so that their cured films have a cross-linked structure without producing by-products.
Second, there should be no migration of chemical materials, such as amines or acids, into and from the anti-reflective coatings. If acids are migrated from the coatings, the photosensitive patterns are undercut while the egress of bases, such as amines, causes a xe2x80x9cfootingxe2x80x9d phenomena.
Third, faster etch rates should be realized in the anti-reflective coatings than in the upper photosensitive film, allowing an etching process to be conducted smoothly with the photosensitive film serving as a mask.
Finally, the organic anti-reflective coatings should be as thin as possible while playing an excellent role in preventing light reflection.
As varied as anti-reflective coatings are, those which are satisfactorily applied to submicrolithographic processes using ArF light have not been found, thus far. As for inorganic anti-reflective coatings, there have been reported no materials which can control interference at the wavelength of ArF light, that is, 193 nm. As a result, active research has been conducted to develop organic materials which can form superb anti-reflective coatings. In fact, in most cases of submicrolithography, the coating of photosensitive layers is necessarily accompanied by the coating of organic anti-reflective layers which prevent the standing waves and reflective notching occurring upon light exposure and eliminate the influence of back diffraction and reflective light from lower layers. Accordingly, the development of such anti-reflective coating materials showing high absorption properties at specific wavelengths is one of the hottest and most urgent issues in the art.
The present invention overcomes the problems encountered in the prior art and provides a novel organic compound which can be used in an anti-reflective coating for submicrolithography processes using 193 nm ArF and 248 nm KrF lasers.
The present invention provides a method for preparing an organic compound which prevents the diffusion and reflection caused by light exposure in submicrolithography process.
The present invention further provides an anti-reflective coating composition containing such a diffusion/reflection-preventive compound and a preparation method therefor.
The present invention also provides an anti-reflective coating formed from such a composition and a preparation method therefor.
The present invention pertains to acrylate polymer resins (also referred to herein as xe2x80x9cpolymersxe2x80x9d or xe2x80x9cresinsxe2x80x9d) which can be used as an anti-reflective coating. The polymer resins contain a chromophore which shows high absorbance of light having wavelengths of 198 nm and 248 nm. In addition, a cross-linking mechanism between alcohol groups and other functional groups is introduced into the polymer resins, so that a cross-linking reaction takes place when the coatings of the polymer resins are xe2x80x9chard baked,xe2x80x9d i.e., heated at a temperature of 100-300xc2x0 C. for 10-1,000 seconds. As a result, a great improvement can be effected in the formation, tightness and dissolution properties of the anti-reflective coatings. Particularly, maximal cross-linking reaction efficiency and storage stability are realized in the practice of the present invention.
The anti-reflective coating resins of the present invention have superior solubility in all hydrocarbon solvents, in order to form a coating composition, yet are of such high solvent resistance after hard baking that they are not dissolved in any solvent at all. These advantages allow the resins to be coated without any problem to form an anti-reflective coating which prevents undercutting and footing problems when images are formed on the overlying photosensitive layer. Furthermore, coatings made of the acrylate polymers of the invention are higher in etch rate than the photosensitive film coatings, thereby improving the etch selection ratio therebetween.
The acrylate polymer resins according to the present invention are represented by the following chemical formulas 1 and 2: 
wherein,
Ra, Rb, Rc Rd each is hydrogen or a methyl group;
R1 to R9, which are the same or different, each represents hydrogen, hydroxy, methoxycarbonyl, carboxyl, hydroxymethyl or a substituted or unsubstituted, linear or branched C1-C5 alkyl or alkoxyalkyl;
w, x, y and z each is a mole fraction in the range from 0.01 to 0.99; and
m and n each is an integer of 1 to 5.
The polymers of the present invention are designed to show high absorbance at 193 nm and 248 nm wavelengths. To accomplish this result, a chromophore substituent which is able to absorb light at a wavelength of 193 nm as well as 248 nm is grafted to the backbone of the polymer.
The polymer of chemical formula 1 can be prepared by polymerizing a 9-anthraldehydeoximacrylate-type monomer, a hydroxy alkyl acrylate-type monomer, and a glycidyl acrylate-type monomer with the aid of an initiator in a solvent. Each of the monomers has a mole fraction ranging from 0.01 to 0.99, preferably 0.1 to 0.9.
The polymer of chemical formula 2 can be prepared by polymerizing a 9-anthraldehydeoximacrylate-type monomer, a hydroxy alkyl acrylate-type monomer, a glycidyl acrylate-type monomer and a methyl methacrylate-type monomer at a mole fraction of 0.01 to 0.99 for each monomer, preferably 0.1 to 0.9.
For initiating the polymerization reaction to prepare the polymers of the chemical formulas 1 and 2, ordinary radical initiators may be used, preferably one selected from the group consisting of 2,2-azobisisobutyronitrile (AIBN), acetylperoxide, laurylperoxide and t-butylperoxide. Also, ordinary solvents may be used for the polymerization, preferably a solvent selected from the group consisting of tetrahydrofuran, toluene, benzene, methylethyl ketone and dioxane.
Preferably, the polymerization of the polymers of chemical formulas 1 and 2 is carried out at 50xc2x0-90xc2x0 C.
The present invention also pertains to an anti-reflective coating composition which comprises a polymer of chemical formula 1 or 2 in combination with at least one additive selected from the group consisting of the anthracene derivatives shown in Table 1, below:
In Table 1, R11, R12, R13, R14 and R15 independently represent hydrogen, hydroxy, hydroxymethyl, or substituted or unsubstituted linear or branched C1-C5 alkyl or alkoxyalkyl.
An anti-reflective coating composition according to the present invention may be prepared by adding a compound selected from Table 1, at an amount of 0.1 to 30% by weight, to a solution of a polymer of the chemical formula 1 or 2 in a solvent, and then filtering the resultant solution. This coating composition is applied on a wafer that is then hard-baked to form a cross-linked anti-reflective coating. Semiconductor devices can then be fabricated therefrom.
Ordinary organic solvents may be used in preparing the composition, with preference given to one selected from the group consisting of ethyl 3-ethoxy propionate, methyl 3-methoxy propionate, cyclohexanone and propyleneglycol methyletheracetate. The solvent is preferably used at an amount of 200 to 5000% by weight based on the weight of the anti-reflective coating polymer resin used.
It has been found that anti-reflective coatings of the present invention exhibit high performance in submicrolithographic processes using 248 nm KrF, 193 nm ArF and 157 nm F2 lasers as light sources. The same is also true when electron beams, EUV (extremely ultraviolet) and ion beams are used as light sources.